1. Field of the Invention
This invention relates generally to automotive aftermarket equipment, and more specifically, to a kit of components making up an independent front suspension system for an automobile. Automotive suspension systems of the type using MacPherson struts may be replaced by the invention presented herein to provide an improved, fully independent, double A-arm type of front suspension.
2. Description of the Prior Art
In the evolution of the modern automobile, the proper handling characteristics of the vehicle have become increasingly more important. Automobile manufacturers attempt to design the suspension system to provide predictable steering input, while at the same time recognizing that production vehicles are used by a broad range of drivers. Also important to automobile manufacturers are cost, reliability and ease of repair. Thus, manufacturers of modern automobiles attempt to balance many factors in designing suspension systems, which often results in compromises in certain areas.
One type of steerable front suspension is a "double wishbone" system. In this commonly used system, a lower A-arm, the first of the two "wishbones" comprising the "double wishbone," is pivotally connected to a suspension mounting location at the front of the vehicle. An upper A-arm forms the second "wishbone," and is connected to a second attachment point. A pivoting vertical spindle connects the upper and lower A-arms at their outboard ends, and usually includes a hub to which the wheel and brake components are attached. Typically, a steering arm controllably pivots the spindle between upper and a lower balljoints. An alternative embodiment is the use of a king pin, which is an older method of providing pivoting capability, between the upper and lower A-arms. A spring and shock absorber are associated with one or both of the A-arms to provide support for the vehicle and damping of the spring. A sway bar is also usually attached to the lower A-arm of both front wheels, and depending on its adjustment, can prevent the suspension from moving in opposite vertical directions relative to the frame.
Because of the independent adjustability of both the upper and lower A-arms, the front suspension characteristics for automobiles with wishbone-type suspension can be specifically tuned to optimize performance over a wide variety of conditions. In particular, in high-performance applications such as automobile racing, it is common to tune the camber, castor, bump-steer, Ackerman and other suspension characteristics by carefully aligning the upper and lower A-arms relative to the vehicle frame for specific race track or road conditions.
A second common type of suspension system is the "MacPherson strut" system. A MacPherson strut suspension system uses a lower control arm and a vertical strut that incorporates a spring, a shock absorber and an upper and a lower bearing assembly that allows the strut to rotate responsive to steering input. The lower control arm is typically mounted at its inboard region to the automobile frame, and the upper portion of the strut is usually mounted to a region of the automobile body above and inboard of the wheel well. The MacPherson strut suspension arrangement is generally viewed as a utility suspension that can be made inexpensively, and provides adequate handling in a "street" vehicle. It is especially useful in front-wheel drive vehicles, where its compactness allows space for drive shaft connections to the wheel assembly. It is also relatively inexpensive to manufacture in comparison to the double-wishbone system discussed above.
However, the use of the MacPherson strut suspension arrangement does not provide optimum handling characteristics for high-performance applications. In particular, it is well known that the range of adjustability for MacPherson strut suspension systems are somewhat limited, particularly in the area known as "bump steer" (i.e., change in toe or camber as the wheel travels through varying "bump" and "droop" conditions). Thus, in high-performance applications, the use of a MacPherson strut is not desirable, and is considered inferior to the double A-arm or double-wishbone type of suspension.
Unfortunately, many automobiles that are sold as "high-performance" vehicles include MacPherson strut front suspensions, primarily because the manufacturer desires to save cost. One such automobile is the late model Ford Mustang made from 1979 through to the present. The Ford Mustang is a popular, rear-drive, high-performance street vehicle that is sold in large numbers and includes the undesirable MacPherson strut front suspension. Because the Mustang is a rear-wheel drive vehicle, there is no reason other than cost-saving for including the inferior MacPherson strut front suspension instead of the double A-arm suspension.
Thus, the need exists to provide a cost-effective conversion kit that allows the MacPherson strut front suspension on rear-wheel drive vehicles, such as the late model Ford Mustang, to be easily converted to the double-wishbone A-arm type of suspension.